Autism is a disorder deflned by altered engagement with the social worid that emerges at eariy stages ofthe disorder. Thus, increase knowledge on the crifical periods of typical development during which these eariy social skills emerge and mature and on the underiying neurobiological systems that underiie these skills will give unprecedented opportunity to further understand the neurobiological source of the eariy diagnosis markers of autism. Although research examining the precursors of human social abilities during eariy infancy has significantly increased in the last few years, critical information on the neural substrates that support these eariy developing social skills is still lacking. One ofthe main reasons being the limitafions in neuroimaging the human brain in infancy, and to study brain-behavior relafionship across development using longitudinal studies. Thus, knowledge in this domain must emerge from translational research examining both human populafions and animal models. Rhesus monkeys provide a remarkable opportunity in this domain given (1) the rich and complex social structure in which they develop and navigate, (2) the progressive development of the basic social skills required to develop normal social relationships, and (3) the similarity with humans in brain and cognitive functions development. Thus, Aim 1 will follow longitudinally the development of social visual engagement processes, including attenfion to, detection and integrafion of social signals in normally developing rhesus monkeys from birth to 6 months, using neuropsychological marker tasks similar to those employed in the typical and atypical human population (Project I) to facilitate cross-species comparisons. This will allow defining significant crifical periods during which these processes emerge and refine. Aim 2 will investigate in the same animals the maturafional changes in brain networks mediafing these basic social processes using noninvasive neuroimaging procedures. These studies on the normally developing rhesus monkeys will provide unparalleled information and a critical non-human primate model that could be used for further invesfigafions targeting gene-behavior relafionships and therapeutic intervenfions. RELEVANCE (See instructions): This multifaceted project will provide much needed normative data on the development of social engagement and ecologically valid procedures to be used to assess the phenotype of transgenic monkeys and validate their relevance as an animal model of autism (Project IV) and in future studies to assess potential treatment. This innovafive project will significantly impact studies of the causes, neural bases, and potential treatment not only for autism but also for other human developmental disorders associated with atypical social skills.